The use of catalyst in a distillation column to concurrently carry out chemical reactions and separate the reaction products has been practiced for some time. This use of a catalytic distillation column reactor lends itself particularly well for reversible reactions in the liquid phase. See for example U.S. Pat. Nos. 4,336,407 (etherification), 4,482,775 (isomerization), 4,242,530 (separation of isobutene from C.sub.4 streams) and 4,551,567 (deetherification). The combination is useful because the reactants, in the liquid phase are quickly separated from the reaction products due to boiling point differences by fractional distillation. Thus the reverse reaction is suppressed.
There have been disclosed several different arrangements to achieve the desired result. For example British Patents 2,096,603 and 2,096,604 disclose placing the catalyst on conventional trays within a distillation column. A series of U.S. patents, including those listed above commonly assigned with the instant invention discloses using the catalyst as part of the packing in a packed distillation column. More particularly U.S. Pat. Nos. 4,443,559 and 4,215,011 exemplify the latter.
Where the catalyst is used as distillation packing, it is usually contained in some cloth belt or wire mesh baskets. Additionally U.S. Pat. Nos. 4,443,559 and 4,215,011 disclose a particulate resin catalyst contained in pockets on a cloth belt. The cloth belt is arranged and supported in the column by wire mesh intimately associated with the cloth pockets. U.S. Pat. Nos. 4,439,350 and 4,536,373 disclose apparatus for placing the cloth belts containing the catalyst on conventional distillation column trays.
It is generally recognized that ion exchange resin catalyst must be in small particulate form. See for example, "Catalytic reaction in Ion Exchange Columns Whilst Displacing the Chemical Equilibrium," Chemiker-Zeitung/Chemische Apparatur, Vol. 90, Nov. 13, 1966, and German Patent 1,075,613. The small particulate form necessitates the bags or wire mesh containers in order to prevent undue pressure drop and provide sufficient space for liquid/vapor flow in the column.
While ion exchange resins have many applications as catalysts, in some applications they become deactivated quickly. Additionally, the catalyst may age at different rates up and down the column. At some point in time the catalyst, or some portion of it, must be replaced or regenerated. In all prior arrangements the distillation column must be shut down, either for regeneration in situ or for removal of the deactivated catalyst. Removal and replacement of the catalyst can be cumbersome and time consuming even though provision may be made for removing and replacing only a portion of the catalyst.
The inventor has thus seen a need for a method and apparatus for removing and replacing catalyst without stopping operation. Such a method and apparatus would make many more applications of ion exchange resin catalysts economically feasible.